The present invention relates to an outline data image drawing apparatus which generates a desired dot pattern for, e.g., filling up a pattern such as a graphic FIGURE on the basis of raster information.
In conventional outline data image drawing apparatuses, only the changing points, at which an outline is, undergoing a change of its coordinate in the predetermined one axis direction (i.e., X or Y direction), are stored in an image memory when the apparatus draws an outline (contour) of a graphic FIGURE or the like. When the apparatus performs a pattern-filling operation, data is inverted each time the scanning in the image memory along the other axis encounters a changing point.
For example, when an outline data image drawing apparatus of the above type draws an outline of a triangular form as shown in FIG. 14(a) into its image memory, only the changing points in relation to, for example, the Y axis are stored in the image memory as shown in FIG. 14(b). In performing an operation of filling up a pattern with dots, the scanning is performed along the X direction in the image memory in which an image has been drawn, as illustrated in FIG. 14(b). When the scanning along for example, the line "b" reaches the changing point b1, data "1" (or "0") is set to start the filling. Then, when the scanning reaches the next changing point b2, data is inverted to "0" (or "1") to finish the filling. Thus, the triangular FIGURE shown in FIG. 14(a) is filled up with dots as shown in FIG. 14(c) by performing the pattern filling operation with respect to individual lines along the X direction in the image memory. In FIG. 14, each point is filled with a dot when the data is at "1".
However, the conventional outline data image drawing apparatus mentioned above draws outlines in such a memory as illustrated in FIG. 15(b) into the image memory, since it stores only the changing points of the image drawing direction in relation to, for example, the Y axis. (The original outlines are overlapped with each other as shown in FIG. 15(a).) When a pattern filling operation is performed by scanning such an image, which has been drawn in the image memory, the apparatus starts pattern filling by shifting the data from "0" to "1" when the scanning reaches the first changing point b1 on the line b, stops pattern filling by inverting the data from "1" to "0" when the scanning reaches the changing point b2, further resumes pattern filling by inverting the data from "0" to "1" when the scanning reaches the changing point b3, and then finishes pattern filling when the scanning reaches the final changing point b4. The apparatus thereafter proceeds to the execution of the pattern filling operation of the next line. Therefore, the conventional outline data image drawing apparatus has a shortcoming that it is incapable of achieving an accurate pattern filling operation in relation to the original graphic FIGURES, since the area where outlines overlap with each other escapes from the pattern filling operation as shown in FIG. 15(c).
Also, since only the changing points in relation to the X or Y direction of outlines are stored in the image memory, it is not possible to extract only the outlines.